Note 10 - Fair Value Measurements - Financial Assets and Liabilities, Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Total Fair Value	$ 471,340	$ 466,439
Assets, fair value	518,454	510,372
Fair Value, Inputs, Level 1 [Member]
Assets, fair value	88,340	59,395
Fair Value, Inputs, Level 2 [Member]
Assets, fair value	428,598	449,266
Fair Value, Inputs, Level 3 [Member]
Assets, fair value	1,516	1,711
Money Market Funds [Member]
Total Fair Value	41,226	15,462
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	41,226	15,462
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	0	0
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Total Fair Value	0	0
Certificates of Deposit [Member]
Total Fair Value	131,042	130,467
Certificates of Deposit [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	0	0
Certificates of Deposit [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	131,042	130,467
Certificates of Deposit [Member] | Fair Value, Inputs, Level 3 [Member]
Total Fair Value	0	0
Corporate Debt Securities [Member]
Total Fair Value	244,155	292,586
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	0	0
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	244,155	292,586
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Total Fair Value	0	0
Commercial Paper [Member]
Total Fair Value	18,163	17,928
Commercial Paper [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	0	0
Commercial Paper [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	18,163	17,928
Commercial Paper [Member] | Fair Value, Inputs, Level 3 [Member]
Total Fair Value		0
US Government Agencies Short-Term Debt Securities [Member]
Total Fair Value	35,238	8,285
US Government Agencies Short-Term Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	0	0
US Government Agencies Short-Term Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	35,238	8,285
US Government Agencies Short-Term Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Total Fair Value	0	0
Auction Rate Securities [Member]
Total Fair Value	1,516	1,711
Auction Rate Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	0	0
Auction Rate Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	0	0
Auction Rate Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Total Fair Value	1,516	1,711
Mutual Fund [Member]
Total Fair Value	47,114	43,933
Mutual Fund [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	47,114	43,933
Mutual Fund [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	0	0
Mutual Fund [Member] | Fair Value, Inputs, Level 3 [Member]
Total Fair Value	$ 0	$ 0